[nascarnation]

A compression test is a good non-invasive start:

http://www.youtube.com/watch?v=myuzWaXSdw4

[Blueflag]

True. I used to make beer money in college as a British Leyland mechanic. A leak-down was one of my first tests, after watching the tailpipe on throttle up, then throttle-lift ... rings or valve guides - which would it be? ;-)

[wjcsux]

I agree. Compression test is the first place to start.